1. Field of the Invention
The present invention relates to an electronic control apparatus mounted in a vehicle or the like, and particularly to improvement of a signal communication circuit situated between an intelligent power module including a plurality of opening/closing devices, a multi-channel A/D converter, and a serial-parallel converter and a microprocessor that collaborates with the intelligent power module.
2. Description of the Related Art
With regard to an electronic control apparatus mounted in a vehicle or the like, there is publicly known an electronic control apparatus in which a plurality of opening/closing devices that are supplied with electric power from an external power source and perform energization drive of a plurality of electric loads, respective excess current cutoff circuits and overheat shutoff circuits for the opening/closing devices, and an abnormality detection circuit are integrated and are connected in series with a microprocessor by way of a serial-parallel converter.
For example, Patent Document 1 [Japanese Patent Application Laid-Open No. 2002-0273665 (FIG. 1 and ABSTRACT OF THE DISCLOSURE)] discloses an “intelligent power module” in which there are provided a power semiconductor switching device; a driving means for the power semiconductor switching device; an abnormality detection means that detects a fatal abnormality and a precursory abnormality, which occurs prior to the fatal abnormality, in the switching device or the driving means; a protection means that protects the switching device when the abnormality detection means detects an abnormality; and an abnormality output means that outputs a signal based on an abnormality detection signal from the abnormality detection means. The intelligent power module is characterized in that the abnormality output means outputs an abnormality cause discrimination signal, as a serial signal, that indicates the cause of a fatal abnormality or a precursory abnormality. The cause of an abnormality can be discriminated without providing a great number of output terminals; thus, there can be provided an inexpensive intelligent power module.
It is also publicly known that an A/D converter is provided in an intelligent power module. For example, Patent Document 2 [Japanese Patent Application Laid-Open No. H07-115354 (FIG. 1 and ABSTRACT OF THE DISCLOSURE)] discloses an “intelligent power module” in which there are provided a power amplification semiconductor device; a temperature detection device that detects the temperature of the power amplification semiconductor device; and a temperature information output means that outputs temperature information detected by the temperature detection device, as either a continuous signal or a digital signal generated by A/D-converting the continuous signal. The intelligent power module is characterized in that, when the intelligent power module is overloaded and the temperature of the power amplification semiconductor device rises, it is made possible to limit the overload imposed the intelligent power module by utilizing temperature information detected by the temperature detection device, before the temperature of the power amplification semiconductor device reaches the point at which the power supply to the power amplification semiconductor device cannot help being turned off, and the intelligent power module can continue to operate with the limited load.
Furthermore, it is also publicly known that an opening/closing control signal, as a serial signal, is transmitted to the intelligent power module. For example, Patent Document 3 [Japanese Patent Application Laid-Open No. H05-262190 (FIG. 1 and ABSTRACT OF THE DISCLOSURE)] discloses a “total control apparatus for an automobile” in which a parallel output signal generated by a control unit in the total control apparatus is converted into a serial signal and transmitted to an intelligent power module, and then the intelligent power module converts the serial signal into a parallel signal so as to drive a plurality of actuators; thus, there can be provided a total control apparatus in which the number of wiring leads is reduced, the control unit is downsized, and the reliability of the total control is raised.
Meanwhile, Patent Document 4 [Japanese Patent Application Laid-Open No. H08-308238 (Table 1 and Paragraph [0009])] discloses a “PWM signal output apparatus and method” in which the active level width of a PWM signal is converted into the number of clock pulses of logic “1”, sent out during one cycle of the PWM signal, so that there is outputted a PWM signal having a desirable duty ratio. Specifically, in the case where there is outputted a PWM signal in which the number of bits per one cycle is 72 and the duty ratio is 30%, 30% of 72 bits are set to “1” and the rest of them are set to “0”.
Furthermore, in Non-Patent Document 1 [Data Sheet of “TLE6220GP-type smart switch” manufactured by Infineon] that discloses a “TLE6220GP-type smart switch”, there is described the specification of a semiconductor product that includes four opening/closing devices, an abnormality detection circuit, an excessive-current protection circuit, and a serial-parallel converter and that can perform opening/closing control of the opening/closing devices by utilizing a serial control signal or a parallel control signal; it is described that the parallel control signal is applied to pulse-width modulation control; and it is described that disconnection/shortcircuit abnormality information on the opening/closing device can be monitored through the serial-parallel converter.
In the “intelligent power module” disclosed in Patent Document 1, the respective cause-discriminated abnormality occurrence statuses of the plurality of switching devices can be read through a serial signal and hence the number of input signals of, for example, a microprocessor that is concurrently utilized can be suppressed; however, because it is required to supply a control signal to each opening/closing device, there is posed a drawback that the number of the outputs of the concurrently utilized microprocessor cannot be suppressed, even in the case of a simple application where part or all of the opening/closing devices perform opening/closing operation at low frequency.
In the “intelligent power module” disclosed in Patent Document 2, temperature information on the opening/closing device can be read by, for example, a concurrently utilized microprocessor; however, there is posed a drawback that, when an A/D converter is provided in the intelligent power module, the number of input terminals of the microprocessor is increased due to reading of the digital value of the temperature information.
Furthermore, in the “total control apparatus for an automobile” disclosed in Patent Document 3, even though the number of the wire leads for opening/closing signals can be reduced in an application where a great number of opening/closing devices are simply opening/closing-controlled; however, in the case of an opening/closing device that needs to perform high-speed operation such as pulse-width modulation control and pulse output control, there is posed a problem that the responsiveness to a serial signal is insufficient.
In addition, in the “PWM signal output apparatus and method” disclosed in Patent Document 4, it is proposed that pulse-width modulation control be performed through a serial signal; however, in this case, there is posed a problem that the number of signal wire leads cannot be reduced because serial signal lines are required, and there is also posed a drawback that, because ON period or OFF period concentrates in the ON/OFF control period, the fluctuation in the load current becomes large.
In the “smart switch” disclosed in Non-Patent Document 1, as the control signal for the opening/closing device, a serial control signal or a parallel control signal can selectively be utilized, and overheating can be prevented by an excessive-current protection circuit in which the rated current of the opening/closing device is adopted as a reference; however, because there is provided no function for monitoring a detected load current through A/D converter, there is posed a drawback that overload detection where the rated current of an applied load is utilized as a reference cannot be performed. Moreover, there is posed a problem that, in the case where pulse-width modulation control is performed through a parallel control signal, the digitally converted value cannot simply be read as a serial signal, even if an A/D converter is incorporated therein.